Simplify Texture Keyframes
At the bottom of the image node you will see, "Single Image", change this to "Image Sequence" and fill in the number of frames. While the render preview in the viewport doesn't usually update as you change frames it does update when you do a proper render.



The catch with this is that the each image is expected to be named with its numerical sequence, eg. "display001.png" "display002.png" "display003.png". If a number is missing then you get no texture. You can make one image last for several frames by creating symbolic links for the missing files, that is if you make a link to "display002.png" and name it "display003.png" then the same image will be shown for two frames.

Here is a python script that can create symlinks for the missing images in a sequence. So you can name your images "display0001.png" and "display0005.png" and the script will make links so that the first image is also used for frames two to four.